1. Field of the Invention
The invention relates to reclamation of relatively low boiling point solvents when such solvents are contaminated from prior use and/or manufacturing processing. In particular, the invention relates to the solvent recovery of tetrahydrafuran (THF) when formed with other particulate and chemical contaminants into a sludge-like waste product.
2. Description of the Prior Art
Many solvents of relatively low boiling point are utilized in manufacturing processes, and by their use they become contaminated commonly with particulates and other chemicals. Often such solvents are flammable, toxic, and dissolve many organic materials with which they come in contact. Thus, their disposition as a waste product presents serious problems from both an environmental and a waste-hauling standpoint. Moreover, many solvents are derived from hydrocarbon materials which are becoming increasingly expensive to procure, if available at all. Thus, a need exists to extract spent solvents which have become contaminated from waste materials and recycle such solvents back to relatively pure status.
In particular, THF is a solvent used in many industrial processes. In one instance, THF is utilized as a solvent carrier in the manufacture of magnetic recording media. In producing such magnetic recording media including flexible disks, cassettes, data recording cartridges, and other media devices, THF is mixed with other materials including iron oxide particles and resins to form a liquid within which such particles are evenly dispersed. This liquid is used for coating suitable substrates. In the coating process, relatively large filter housings hold the liquid or "ink" prior to being pumped into the coating station. Such filter housings retain a residue on the order of several gallons of ink per filling which is left as a sludge at the bottom of the container. In addition, THF is used as a solvent to clean parts on the magnetic media coating line. Thus, a significant amount of contaminated THF is generated often in the form of a thick slurry or so-called "slop".
In the prior art THF has been extracted from such "slop" by use of a container having hot water therein maintained at a temperature less than 100.degree. C. (the boiling point of water) but greater than 66.degree. C. (the boiling point of THF). Theoretically, the "slop" is supposed to contact the hot water and have the THF driven off in the form of vapors which can be collected and condensed to form a mixture of THF plus water. This liquid can thereafter be further purified by known techniques. In practice, this process is extremely inefficient. By its nature, the "slop" contains a significant quantity of binder material and cross linking material which is used in the formation of the magnetic media. When the binder and cross linking material hits the hot water, the temperature is high enough so that the binder cures and tends to encapsulate significant amounts of THF within small nodules. Efficiencies for this prior art process are in the range of 40% to 50% yield as a percentage of the total THF contained within the raw "slop".